No full-text available
To read the full-text of this research,
you can request a copy directly from the author.
Modelling Chemical and Physical Processes of Wood and Biomass Pyrolysis
Abstract
This review reports the state of the art in modeling chemical and physical processes of wood and biomass pyrolysis. Chemical kinetics are critically discussed in relation to primary reactions, described by one- and multi-component (or one- and multi-stage) mechanisms, and secondary reactions of tar cracking and polymerization. A mention is also made of distributed activation energy models and detailed mechanisms which try to take into account the formation of single gaseous or liquid (tar) species. Different approaches used in the transport models are presented at both the level of single particle and reactor, together with the main achievements of numerical simulations. Finally, critical issues which require further investigation are indicated.
... Experimental methods provide valuable insights but are often limited in scope due to the complex interactions between the gas and solid phases and the high-density flow of particles. As a result, reactor design and optimization have traditionally relied on empirical correlations and pilot-scale studies [7][8][9]. Recent advancements in computational fluid dynamics (CFD) offer a powerful tool to overcome these limitations. CFD models enable the simulation of detailed transport processes and chemical reactions, facilitating reactor optimization with reduced experimental costs. ...
... The kinetics of the process depend on the composition of the biomass material to be pyrolyzed. There are several ways of establishing the sequence of chemical reactions and the main components to be considered in a way that is computationally affordable [7,[47][48][49]. In this work, bagasse and red oak are considered as the pyrolyzing material, and the kinetics previously reported by Bradbury et al. [50], and subsequently adapted by Di Blasi [7], Miller and Bellan [47], are adopted as a first approach. ...
... There are several ways of establishing the sequence of chemical reactions and the main components to be considered in a way that is computationally affordable [7,[47][48][49]. In this work, bagasse and red oak are considered as the pyrolyzing material, and the kinetics previously reported by Bradbury et al. [50], and subsequently adapted by Di Blasi [7], Miller and Bellan [47], are adopted as a first approach. In this context, the virgin biomass, composed of cellulose (C), hemicellulose (H), and lignine (L), reacts until it becomes active biomass. ...
This study investigated the fast pyrolysis of biomass in fluidized-bed reactors using computational fluid dynamics (CFD) with an Eulerian multifluid approach. A detailed analysis was conducted on the influence of various modeling parameters, including hydrodynamic models, heat transfer correlations, and chemical kinetics, on the product yield. The simulation framework integrated 2D and 3D geometrical setups, with numerical experiments performed using OpenFOAM v11 and ANSYS Fluent v18.1 for cross-validation. While yield predictions exhibited limited sensitivity to drag and thermal models (with differences of less than 3% across configurations and computational codes), the results underline the paramount role of chemical kinetics in determining the distribution of bio-oil (TAR), biochar (CHAR), and syngas (GAS). Simplified kinetic schemes consistently underestimated TAR yields by up to 20% and overestimated CHAR and GAS yields compared to experimental data (which is shown for different biomass compositions and different operating conditions) and can be significantly improved by redefining the reaction scheme. Refined kinetic parameters improved TAR yield predictions to within 5% of experimental values while reducing discrepancies in GAS and CHAR outputs. These findings underscore the necessity of precise kinetic modeling to enhance the predictive accuracy of pyrolysis simulations.
... However, most experimental apparatus currently available do not meet these requirements. Common devices used to study MSW pyrolysis include thermogravimetric analyzers (TGAs) [13,[15][16][17], drop tube furnaces [21,22], and fluidized bed reactors [23]. A TGA [13,[15][16][17] is a commonly applied device to conduct MSW pyrolysis studies due to its high level of automation and measurement resolution. ...
... Common devices used to study MSW pyrolysis include thermogravimetric analyzers (TGAs) [13,[15][16][17], drop tube furnaces [21,22], and fluidized bed reactors [23]. A TGA [13,[15][16][17] is a commonly applied device to conduct MSW pyrolysis studies due to its high level of automation and measurement resolution. The maximum heating rate of a conventional TGA is generally below 120 K/min [15,16]. ...
... A TGA [13,[15][16][17] is a commonly applied device to conduct MSW pyrolysis studies due to its high level of automation and measurement resolution. The maximum heating rate of a conventional TGA is generally below 120 K/min [15,16]. Some studies have mentioned that certain advanced TGAs can achieve heating rates as high as 500 K/min [13,17]. ...
The pyrolysis of municipal solid waste (MSW) is an efficient, cost-effective, and environmentally beneficial thermochemical treatment method. A macro thermogravimetric analyzer (Macro TGA) was used to study the pyrolysis behavior of cedar and polyethylene (PE) at slow (10 K/min) and fast (700, 800, and 900 °C) heating rates. For cedar, the pyrolysis rate curve showed multi-peak characteristics at the slow heating rate and single-peak characteristics at the fast heating rate. Conversely, PE exhibited the opposite behavior. At fast heating rate of 700 °C, the pyrolysis rate for cedar increased from 0.685 to 0.847 min−1 as the sample temperature rose by over 100 °C, from 351 to 455 °C. By contrast, for PE, the rate increased from 0.217 to 1.008 min−1 with a smaller temperature rise of less than 30 °C, from 630 to 656 °C. According to the International Confederation for Thermal Analysis and Calorimetry (ICTAC) guidelines for analyzing pyrolysis thermogravimetric data, cedar pyrolysis primarily followed a single-step parallel reaction pathway, while PE exhibited some multi-step parallel reactions. A newly developed discrete distributed activation energy model (DDAEM), along with the traditional iso-conversional model (ICM) and distributed activation energy model (DAEM), were applied to predict pyrolysis characteristics at fast heating rates. For cedar, both DDAEM and ICM provide accurate predictions, with average activation energies calculated by these two models being 48.08 and 66.37 kJ/mol, respectively. For PE, DDAEM demonstrates significantly higher predictive accuracy than ICM, particularly when the conversion is below 0.2. As the pyrolysis conversion of PE increases from 0.25 to 0.65, the average activation energy calculated using ICM was found to be 58.32 kJ/mol. By contrast, for DDAEM, the activation energies for the first and second step reactions were 110 and 60 kJ/mol, respectively. This indicates that ICM can only calculate the activation energy for the final step and not for the rate-limiting step. For both cedar and PE, DAEM fails to provide accurate predictions due to the unsteady heating rate.
... Pyrolysis parameters are frequently determined with a one-component approach, generally through model-free fitting and isoconversional methods (Dhaundiyal, Mohammad, and Laszlo 2019;Mishra and Mohanty 2018;Yan et al. 2020). However, biomass pyrolysis should be modeled as a multicomponent process to accurately reproduce experimental data (Di Blasi 2008). Detailed models have been developed, grouping similar components and lumping some reactions, allowing a model capable of satisfactorily describing a variety of biomass pyrolysis (Ranzi et al. 2008). ...
... Theses parameters are used to model one pyrolysis reaction. Modelling biomass pyrolysis as a single reaction usually fails to efficiently reproduce the complex material decomposition (Di Blasi 2008). This work employs a multicomponent reaction, in which each component i is decomposed independently following its own Arrhenius law. ...
... Consistency in results between methods reaffirms their reliability, with variations staying within comparable ranges. DSC measurements allowed to confirm the positioning of pseudo-lignins decomposition peak in regard to the temperature, and also confirmed its exothermic degradation, as showcased by (Di Blasi 2008). ...
... In torrefaction (mild pyrolysis), it is mostly the hemicelluloses which is targeted together with some of the cellulose. Many researchers have studied the impact of these biochemical components on the thermal behaviour of biomass and the global reaction rates are generally wellunderstood [14,15]. Generally, the envelope for hemicelluloses' decomposition is seen in the 180-315 • C temperature range, that for cellulose is 270-370 • C and that for lignin is 160-600 • C [11,16,17]. ...
... Other factors besides the actual nature of the hemicelluloses and lignin polymers affect the decomposition temperature range. While the global decomposition of the polymers is relatively well understood, the detailed decomposition is complex and consists of numerous endo-and exothermic decomposition, rearrangement and condensation reactions [15]. This means that competition between the detailed chemical reactions affects the global reaction rates and heat release as described in Refs. ...
Torrefaction research at an industrial scale is rarely reported in the literature. This study provides a unique combination of 1100 kgh − 1 torrefaction trials for autothermal operation in an industrial setting, with underpinning investigations from laboratory-scale thermogravimetric analysis (TGA). The feedstocks were softwood (pine and spruce) and hardwood (alder and ash) species as well as an herbaceous biomass (Miscanthus). The laboratory results were used to interpret their plant-scale torrefaction profiles and gave key insights on process optimisation and control. Industrial-scale trials on ash wood were challenging due to large fluctuations in both temperature and process gas generation. TGA studies indicated fast rates of torrefaction and a low temperature exotherm for this wood type, which can explain the observed behaviour. The hardwoods achieved autothermal operation in torrefaction more easily than the softwoods, and the Miscanthus showed the most promise for continuous, autothermal production. TGA provided nuanced insights into the relative rates of mass loss, characteristic decomposition temperatures and exo/endothermic thermal behaviours which were able to give perceptive interpretation of the plant scale observations. A dominant factor is the nature and reactivity of the hemicelluloses and the associated low temperature exotherm that exists for some feedstocks, particularly hardwoods. Another factor is the catalytic components, particularly potassium, and their availability to participate in catalytic torrefaction reactions. The novel integrated study highlighted the impact of highly reactive hemicelluloses in scale-up, whereby the small differences in thermochemistry identified by TGA are magnified and affect process control and ease of autothermal operation.
... Some models are so complex that they cannot be solved in a reasonable calculation time or are not transferable due to a lack of consideration of influencing factors [14]. Therefore, several methods to simplify complex chemical reaction systems are known [15]. Nevertheless, most of these models are based on flaming combustion in which the oxidation mainly occurs in the gas phase. ...
... .15 shows the qualitative evaluation of the temperature and mass concentration at different times. Further 2-D planes and an estimation of the radial temperature gradient of the smoldering front are provided in Appendix A.1. ...
Bio-based insulation materials are prone to self-sustained smoldering after ignition. While empirical studieshighlight key factors influencing smoldering initiation and spread, a comprehensive understanding of themechanisms remains incomplete. This study introduces a smoldering model for bio-based insulation materials,integrating flow, heat, and moisture transfer with a 3-step reaction model.Material parameter quantification is demonstrated using wood fiber insulation as a reference, with method-ologies applicable to other materials. Experimental setups for fluid mechanical, thermal, and moisture transportproperties are described, supplemented by data from literature.The modeling framework couples flow, heat, and moisture transport mechanisms with reaction rates depen-dent on temperature and concentration. A diffusion-limiting approach accounts for particle-surface transportconstraints. Implementation is performed using COMSOL Multiphysics ® 6.Validation tests in a 1.5 m tube furnace with controlled heating zones and inflow conditions demonstrate themodel’s ability to accurately predict smoldering velocity. Further optimization is required to improve ignitiontime predictions. While some inhomogeneity effects are not fully captured, the model provides a solid foundationfor further refinement and scaling to component levels.
... Hence the great interest among scientists, with a variety of works in the literature having different kinetic models with the sole aim of understanding the degradation process of wood material [8][9][10][11]. Prakash et al. [12] and Di Blasi et al. [13] summarized several models which have been studied in recent years. Three models stand out from these studies. ...
... The peak for lignin degradation does not appear distinctly in the DTG curves because lignin degrades gradually over a broader temperature range which overlaps with cellulose and hemicelluloses degradation [13,23,33]. ...
A kinetic model based on the two-stage semi-global multi-reaction model of Grioui was developed using the TG and DTG curves for the by-products of Kambala and Ayous. These two tropical species are widely used in the Republic of Congo. The TG and DTG curves were obtained through thermogravimetry at five different heating rates (3, 7, 10, and 20 K/min) up to a final temperature of 800 • C under a nitrogen atmosphere. The thermal decomposition of both species started at similar temperatures, but the profiles exhibited notable differences. Kambala showed a distinct profile with two peaks at approximately 500 • C and 700 • C, which upon further investigation were found to correspond to ash decomposition. Additionally, the shoulder present in Ayous between 250 • C and 300 • C, attributed to hemicelluloses degradation, was absent in the DTG curves for Kambala. The kinetic model for Ayous was formulated in three steps, while the model for Kambala consisted of four steps. Both models accurately predicted the thermal degradation of the wood species, and the resulting kinetic parameters aligned with those reported in the literature.
... A low porosity is associated with high-density particles as with the coal char particle, hence less surface area available for combustion reactions. This assertion is supported by other researchers such as Tang et al. [43] during their studies with demineralised coal, Di Blasi [44] during his pyrolysis studies of wood, and Sadhukhan et al. [45], who focused on large coal particles. As demonstrated in Figure 14, blending increased particle burnout maximum values marginally, though the reaction zone for all the cases was located within the same region. ...
This study focused on evaluating the combustion ignition, burnout, stability, and intensity of Hwange coal and Pinus sawdust blends within a drop tube furnace (DTF) through modelling. The cocombustion of coal with biomass is gaining attention as a strategy to improve fuel efficiency and reduce emissions. Hwange coal, a key energy source in Zimbabwe, produces significant emissions, while Pinus sawdust offers a renewable alternative with favourable combustion properties. Optimising cocombustion performance is highly dependent on understanding various mass- and energy-conservation-related parameters in detail, hence the motivation of this study. The fuels of interest were blended through increasing the Pinus sawdust mass percentages up to 30%. A DTF that is 2 m long and 0.07 m in diameter was modelled and validated successfully using particle residence time and temperature profiles. An increase in blending resulted in an increase in combustion intensity, as made apparent by the heat of reaction profiles, which were also shown to be dependent on the kinetic rate of the reaction between CO and O2 to form CO2. The burnout rate profiles demonstrated that as blending increased, heat was released more abruptly over a short distance; hence, combustion became less stable. The burnout rate profiles were shown to be dependent on the kinetic rate of reaction between char and O2 to form CO. The effect of DTF wall temperatures (1273, 1473, and 1673 K) was also studied, with the results showing that at a low temperature, the reaction zone was delayed to a distance of 0.8 m from the injection point, as compared to 0.4 m at 1673 K. In summary, this study demonstrated that combustion ignition, burnout, and intensity increased with the blending ratio of Pinus sawdust, whilst combustion stability decreased.
... It is performed through thermal decomposition, which involves heating up biomass to high temperatures and breaking down its cellulose, hemicellulose, and lignin components [47]. The effectiveness of thermal breakdown, which takes place in limited oxygen with a temperature varying from 300 and 500°C and depends greatly on the type and properties of the feedstock used [48]. Traditional BC manufacturing processes such steel kilns, earthen, and brick kilns cause air pollution via releasing exhaust volatile matter into the environment. ...
The amelioration of water quality and the effective management of waste are two critical environmental obstacles. Biochar (BC) has the potential to serve as a promising solution for addressing both of these issues. In this regard, this review article elucidates the potential of BC as a sustainable approach to overcome the challenges associated with water remediation and waste management. The study focuses on the biomass-based synthesis of BC and its composites, with optimum experimental parameters (pyrolysis temperature, activation methods, and precursor materials) to enhance the performance. Afterward, the article provides a comprehensive discussion on BC-based water pollutant removal processes (adsorption and advanced oxidation processes) along with the significance of modification strategies. The review also evaluates current BC-based products, discusses their market potential, and identifies key challenges in commercialization. Thus, this article offers new insights into sustainable water remediation and waste management processes by following the principles of sustainable development goals (SDGs).
Graphical Abstract
... Fig. 8, shows the proportion of all 100 solid-phase TCs in Test 1.1 that exceed either 95, 105, or 300 • C. The first two were chosen as ± 5 % of the boiling point of water at 1 atm and represent the plateau observed in Fig. 7. The third threshold of 300 • C is chosen as the commonly utilised temperature to indicate the onset of significant pyrolysis from wood to char [27,28]. Fig. 8 shows that the time for the first significant increase in exceedance of the 95 • C lower bound was approximately 12 min after flashover. ...
This paper seeks to provide key fundamental knowledge underpinning the use of self-extinction principles as part of a design framework for buildings with engineered mass timber structures. The results from six compartment fire experiments in a cross-laminated timber (CLT) enclosure with different ratios of exposed timber are presented and analyzed to establish the effects of timber exposure on the dynamics of a fire and on the potential of the fire to self-extinguish. The results show the relevance of four key parameters that need to be considered concurrently when assessing self-extinction in mass timber compartments: (a) the characteristic time for burnout of the movable fuel load, (b) the characteristic time for the occurrence of char fall-off, (c) the characteristic time for the occurrence of encapsulation failure, and (d) the heat exchange within the compartment after consumption of the moveable fuel. Self-extinction was attained only when the characteristic time for the occurrence of char fall-off was longer than the characteristic time for burn-out and the heat exchange after burn-out resulted in a heat flux below a well-defined threshold. The position of the exposed timber surfaces affected the magnitude of the threshold heat flux. If the characteristic time for burn-out was greater than the characteristic time for encapsulation failure, self-extinction was not observed to occur.
... The fuel conversion in fluidized bed gasification is, to a considerable extent, determined by the fuel pyrolysis [24,127]. In pyrolysis, the large solid fuel molecules are broken down into smaller molecules by thermal cracking of chemical bonds (see section 2.1.1). ...
Sewage sludge is a residue that is generated unavoidably by the population. On a first sight, sewage
sludge may be a hazardous waste that requires safe disposal. By looking closer, it is recognized as
secondary resource. The mineral fraction contains valuable elements such as phosphorous, which
can be retrieved as secondary raw material. This thesis focuses on the organic fraction, which is a
renewable fuel and carbon source and can be used to substitute fossil carbon in fuels and chemicals.
The first step in converting sewage sludge to renewable goods is syngas production via gasification.
The experimental work of this thesis demonstrated the feasibility of synthesis gas production from
sewage sludge by steam-oxygen fluidized bed gasification. It was shown that the process works
reliably in the investigated 20 kW scale and that the syngas contains high H2 and CO concentrations
and is thus suitable for synthesis of fuels and chemicals. The impurities NH3, H2S, COS and tar
species, including heterocyclic species such as pyridine, were measured in considerable concentra�tions in the syngas. Small amounts of limestone bed additive enabled cracking of heavy tars and
partial capture of H2S and COS. It was further found that the cold gas efficiency increases with
rising gasification temperature due to improved tar and char conversion at higher temperatures.
The typical operation temperature 850 °C requires an oxygen ratio of 0.33, obtaining a cold gas
efficiency of 63 %. Moreover, the H2/CO-ratio could be controlled efficiently by altering the steam
to carbon ratio, as steam promotes the water gas shift reaction in the gasifier to achieve the desired
stoichiometry for synthesis, however, resulting in higher energy demand for steam provision. The
experimental results can be utilized for process design, e.g., for a TRL 7-demonstrator.
Furthermore, a gasifier model was developed and an integrated process chain was simulated to
assess the conversion of sewage sludge to synthetic natural gas (SNG) with and without inclusion
of power-to-gas through electrolysis. The total efficiency of the conversion including own con�sumption for the case without electrolysis was 51 % with a carbon utilization of 33 %. These values
could be enhanced by inclusion of power-to-gas. It was predicted that the produced SNG has a
CH4-concentration of between 0.81 m3 m-3
and 0.84 m3 m-3
and nitrogen concentrations of up to
0.16 m3 m-3 originating from fuel-bound nitrogen. The simulations on process integration showed
that up to 20% of the sewage sludge feed can be dried by heat integration. This implies that also
external heat sources have to be used for drying.
Overall, the steam-oxygen gasification proved to be an efficient and technically feasible process for
sewage sludge treatment and can be considered as an alternative to fluidized bed incineration for
future mono-treatment plants.
... Consequently, more pyrolytic gas can be produced by direct solar pyrolysis (through high temperature and fast heating). The outputs, structure and features of the products depend on the pyrolysis parameters.Temperature, heat speed, pressure, [9] and the rate of sweep gas flow is generally considered a secondary paramer[10] as the main pyrolysis parameters. Several scientists have studied pyrolysis parameters in traditional reactors to optimize the output of liquid [11] or char [12]. ...
Concentrated solar energy provides heat to drive biomass pyrolysis reactions, which improves feedstock energy by storing solar energy in chemical types like biogas, biooil, and biochar. Direct solar pyrolysis will produce more pyrolytic gas with a lower heating value due to the high temperature and rapid heating rate.Pyrolysis is one of the methods for extracting energy and useful biomass chemicals. The primary goal of biomass pyrolysis is to produce a liquid fuel that is easier to transport and store and can be used as a substitute for energy. Pyrolysis oil yield and composition are determined by biomass feedstock and operating parameters. It's also crucial to investigate the impact of variables on response performance and the desire to maximize them. The latest biomass pyrolysis literature is used to investigate operating variables.Final pyrolysis temperature, inert gas sweeping, residence times, biomass heating intensity, mineral matter, biomass particle size, and biomass moisture content are the most important operational variables. The aim of this paper is to look into the details of biomass solar pyrolys is using various methods.
... 55 Di Blasi provided similar estimates, with E a values of 80-116 kJ·mol −1 for hemicellulose, 195-286 kJ·mol −1 for cellulose, and 18-65 kJ·mol −1 for lignin. 56 Weeranchanchai et al. demonstrated that the activation energy of biomass pyrolysis, using two parallel reaction models, yields smaller error values compared to the singlereaction kinetic model. 57 Using more specific kinetic parameters for each product therefore improves model accuracy, as reaction kinetic parameters are specific to each reaction. ...
The behavior of biomass pyrolysis can be predicted by analyzing its characteristics. This study aimed to model the release of volatiles across various temperatures, biomass properties, and heating rates. Palm kernel shells were pyrolyzed at 433–773 K with a heating rate of 5 K·min⁻¹ using volatile‐state kinetic modeling. The process began by calculating the biomass type number (NCT), which was used to determine volatile enhancement (VE), volatile release yield (YVY), product yield (Yi), and product mass fraction (yi). The kinetic parameters, including the activation energy for product formation (Eai), were derived through a fitting process.
The results indicate a YVY of 70.77% within the devolatilization zone, corresponding to the degradation of cellulose and hemicellulose. The YVY increased with higher temperatures, lower NCT, and higher heating rates. The activation energy ranged from 155–185 kJ·mol⁻¹ for biocrude oil (BCO) and 149–186 kJ·mol⁻¹ for gas. The kinetic parameters from the volatile‐state kinetic model demonstrated errors below 0.2% in comparison with the experimental data, confirming the model's accuracy and reliability.
... Recently, seaweed hydrolysis achieved convincing results in a two-step microwave treatment, which could provide promising applications in biofuels as well [43]. Currently, microalgae are most commonly used in algal biofuel production, as they have higher lipid contents than seaweed [44][45][46]. The distinctive chemical composition of microalgae cells allows for the extraction of oils and fats through supercritical CO 2 techniques. ...
In this study, a systematic review of algae biofuels, including their development and production process, is presented. Compared with traditional techniques, supercritical CO2 extraction, known for its high efficiency and environmental sustainability, has been widely applied in extracting plant compounds, oils, and fats, demonstrating its role as a promising alternative in biofuel conversion. The principle and features of supercritical CO2 extraction technology are introduced, and its applications in biofuel production in China are reviewed. The results indicate its broad applicability and substantial scientific value in biofuel production, underscored by its unique extraction mechanisms and operational flexibility and obstacles to its large-scale implementation. Against a future where supercritical CO2 extraction will play a pivotal role in industrial biofuel production due to the technology’s advancement and policy support in China, this review offers comprehensive insights and references to guide future research into and practices of supercritical CO2 extraction and biofuel development.
... Burning wood and other cellulosic materials leave behind a char layer that usually shows a distinct pattern of cracks. During combustion, the char acts as a heat barrier between the combustion zone and virgin material, reducing the burning rate of the uncharred material [1]. The shrinkage and cracking of the char layer have been found to influence the pyrolysis [2,3] and the fire resistance of structures made of cellulosic materials. ...
In the assessment of wood charring, it was believed for a long time that physicochemical processes were responsible for the creation of cracking patterns on the charring wood surface. This implied no possibility to rigorously explain the crack topology. In this paper we show instead that below the pyrolysis temperatures, a primary global macro-crack pattern is already completely established by means of a thermomechanical instability phenomenon. First we report experimental observations of the crack patterns on orthotropic (wood) and isotropic (Medium Density Fibreboard) materials in inert atmosphere. Then we solve the 3D thermomechanical buckling problem numerically by using the Finite Element Method, and show that the different crack topologies can be explained qualitatively by the simultaneous thermal expansion and softening, taking into account the directional dependence of the elastic properties. Finally, we formulate a 2D model for a soft layer bonded to an elastic substrate, and find an equation predicting the inter-crack distance in the main crack-pattern for the orthotropic case. We also derive a formula for the critical thermal stress above which the plane surface will wrinkle and buckle. The results can be used for finding new ways to prevent or delay the crack formation, leading to improved fire safety of wood-based products.
... Typically, cellulose decomposition and volatiles release temperature range is 240-350 o C, it is 200-260 o C for hemicellulose and 280-500 o C for lignin [8]. Those volatiles undergo further decomposition that produces CO, CO2, CxHy, and other compounds [9]. Besides volatiles, char is another product of the pyrolysis reaction, which can prevent heat from further penetrating through virgin unburn wood [10]. ...
In recent years, there has been a dramatic increase in façade fires, which brought an urgent demand for relevant research to reduce façade flame spread. As wood has been experiencing a recent renaissance, the investigation of its fire performance and how it can safely be used has become a priority. Wooden components, e.g., balconies and deckings, are widely used as part of buildings and their façades and its preservation by chemical treatment is essential for its protection. Nevertheless, the use of wood preservatives can influence its fire properties. In this work the effect of wood preservatives on wooden decking is experimentally investigated. Emphasis is given to coatings applied after wooden elements are installed as this appears to be the most common practice. Heat release rate and ignition times were recorded for Swedish pine samples coated by three different water-based preservatives and compared with Swedish pine samples with no coatings and with ones treated with fire retardants. Experiments show that composition and concentration of preservatives has an impact on char formation and, in turn, on the fire performance in terms of heat release rate and carbon monoxide (CO) production rate. This could contribute to the façade flame spread rate and can be an added challenge to the evacuation activities.
... Frequency factors were adjusted to match experimental data. R 3 , R 9 , and R 15 (Formation of R-C-K): The activation energy for the rate of formation of R-C-K was estimated to be equivalent to char formation, based on literature data [52]. R 4 (Oxidation of char-bound potassium): The activation energy for the oxidation of char potassium to form potassium carbonate is estimated to be equivalent to the activation energy for the gasification of carbon with carbon dioxide. ...
... Typically, cellulose makes up the largest percentage of the fraction, followed by lignin and hemicellulose [51]. It has been observed that, after moisture removal, the decomposition of the three biomass lignocellulosic components takes place [52]. The use of lignocellulose in H 2 production transformation processes will lower costs while also improving environmental efficiency, reducing the negative consequences of other forms of manufacturing considering the annual production rates of residues extracted from agricultural products [53]. ...
The amounts of H2 production through subcritical water gasification (Sub-CWG) and supercritical water gasification (Super-CWG) have been revealed in the current study. Sunflower waste (SW) was selected as the biomass used in the gasification processes. To determine the fuel characteristics of SW, proximate, ultimate, and higher heating value (HHV) analyses were conducted. The response surface methodology (RSM) was applied to design the experimental runs, to determine and optimize the process parameters, and to explore the interactions between them, which included reaction temperature, feed concentration, and residence time. Furthermore, various catalyst additives (K2CO3, Na2CO3, and NaOH) were used at the optimum level of process parameters to investigate the effect of catalyst on H2 production. According to the results of gasification processes, the amount of H2 production in Sub-CWG was lower when compared to Super-CWG and the main gas yield was CO2 and CH4 due to low reaction temperature and residence time. On the other hand, it has been revealed that Super-CWG is much more efficient in H2 production. Elevated temperatures and extended residence times enhance H2 production by facilitating key reactions such as the water–gas shift and steam reforming. Higher feed concentrations were found to reduce H2 production due to dilution effects and reduced water availability. The RSM explored that the created model matched the experimental data in H2 production since the correlation coefficient values were high enough (R² = 99.83%, R²Adj = 99.52%). In the second part of the study, catalytic Super-CWG experiments were conducted using the optimum process parameters determined by RSM. According to the results, NaOH significantly improves H2 production by enhancing C–C bond cleavage and promoting the water–gas shift reaction, and the mechanistic basis for catalytic activity lies in the reduction of CO and CO2 formation, thus maximizing H2 production.
... The two processes are not clearly separable in a natural setting since the products of one process are linked to and can influence the other process. During pyrolysis, a dead, solid wildland fuel composed of cellulose, hemicellulose, lignin, water and trace elements is heated and breaks down into constituent parts consisting of gases, tars and a solid material called char (Shafizadeh and Fu 1973;Shafizadeh 1982;Di Blasi 2008;Neves et al. 2011). Living wildland fuels additionally contain plant metabolites (Jolly et al. 2012, Matt et al. 2020. ...
Background
Fire models have used pyrolysis data from oxidising and non-oxidising environments for flaming combustion. In wildland fires pyrolysis, flaming and smouldering combustion typically occur in an oxidising environment (the atmosphere).
Aims
Using compositional data analysis methods, determine if the composition of pyrolysis gases measured in non-oxidising and ambient (oxidising) atmospheric conditions were similar.
Methods
Permanent gases and tars were measured in a fuel-rich (non-oxidising) environment in a flat flame burner (FFB). Permanent and light hydrocarbon gases were measured for the same fuels heated by a fire flame in ambient atmospheric conditions (oxidising environment). Log-ratio balances of the measured gases common to both environments (CO, CO2, CH4, H2, C6H6O (phenol), and other gases) were examined by principal components analysis (PCA), canonical discriminant analysis (CDA) and permutational multivariate analysis of variance (PERMANOVA).
Key results
Mean composition changed between the non-oxidising and ambient atmosphere samples. PCA showed that flat flame burner (FFB) samples were tightly clustered and distinct from the ambient atmosphere samples. CDA found that the difference between environments was defined by the CO-CO2 log-ratio balance. PERMANOVA and pairwise comparisons found FFB samples differed from the ambient atmosphere samples which did not differ from each other.
Conclusion
Relative composition of these pyrolysis gases differed between the oxidising and non-oxidising environments. This comparison was one of the first comparisons made between bench-scale and field scale pyrolysis measurements using compositional data analysis.
Implications
These results indicate the need for more fundamental research on the early time-dependent pyrolysis of vegetation in the presence of oxygen.
... For the heat of pyrolysis, both endo-and exothermic values have been reported, although the endothermic processes usually dominate at ambient pressure. 50 For the conditions present in this study, values between 200 kJ/kg and 1.6 MJ/kg were reported for wood 51,52 while for wheat straw, currently no values are available. An accurate estimation is difficult due to a variety of factors influencing the heat of pyrolysis. ...
Chemical looping gasification (CLG) is a novel dual fluidized bed gasification process that enables the conversion of solid feedstocks to a nitrogen-free syngas through in situ air separation, avoiding a costly air separation unit. While there have been recent advances in experimental studies, modeling of CLG is almost exclusively restricted to lab-scale units or 1D models. In this study, a 3D CFD-DEM model of a 1 MWth fuel reactor for the conversion of solid biomass was developed. Due to the high computational demand of the DEM method, a coarse-grained approach was used in combination with a simplified reaction network. The hydrodynamics were modeled with an EMMS drag model. Simulations were conducted for two woody biomasses and wheat straw based on experimental data of a 1 MWth CLG reactor. The model was able to predict the pressure profile over the reactor accurately, with a mean error below 10%. Carbon conversion and oxygen carrier oxidation were in good agreement with the experimental data with mean deviations below 5%, while reasonable values below 8 mol % mean error were achieved for the gas composition. Discrepancies in the gas composition as well as temperature profile indicate that further work is needed in the pyrolysis step of the model.
Smoldering combustion, often linked with forest fires in coniferous forests, pose significant health and environmental risks, particularly in densely populated countries like Germany, where these fires commonly occur in wildland–urban interface (WUI) areas. This study investigates the combustion characteristics of Pinus sylvestris soil, focusing on the underlying processes and thermal behavior. The aim is to provide a comprehensive analysis of smoldering combustion in pine forest soil, with a specific focus on fire‐exposed soil horizons. The research integrates soil characterization, elemental analysis, heat of combustion determination, and thermogravimetric analysis (TGA) of pine soil fractions ranging from < 0.063 to > 4 mm, conducted under both air and nitrogen atmospheres. The derivative thermogravimetry (DTG) curves reveal that the fastest mass loss occurs during pyrolysis, with peak temperatures between 240°C and 280°C. Activation energies ( E a ) were calculated using the Kissinger–Akahira–Sunose (KAS) and Flynn–Wall–Ozawa (FWO) methods. The highest activation energies were observed between conversion rates of 0.2 and 0.4. Activation energies at peak temperatures for all fractions were determined using the Kissinger method. Residue analysis reveals significant variations in organic content, ranging from 22.6% to 92.7%. The findings demonstrate that German‐typical pine soil is prone to smoldering combustion, highlighting processes determined as preheating, drying, pyrolysis, and oxidation. As part of the German Pilot of the EUs TREEADS project, this study provides essential data for numerical simulations, emphasizing the need to consider both physical and chemical properties of soil fractions to mitigate the impact of smoldering fires in pine forest ecosystems.
A comprehensive model for wood pyrolysis has been developed. This model integrates detailed chemical reactions and interactions between chemistry, heat, and mass transfers within the porous medium. The Ranzi’s reaction scheme [1] is well-known for its detailed and comprehensive modelling of wood components (cellulose, hemicellulose, and lignin). This work extends Ranzi’s scheme to include secondary reactions for tars, which cannot be neglected when wood samples behave as thermally thick materials, as is often the case during fire scenarios involving woody materials. A novel aspect of this model is its detailed consideration of gas-solid interactions within wood pores, incorporating mass and heat transfer mechanisms. The model is based on the PATO code (Porous Analysis Toolbox based on OpenFOAM), which treats the porous medium as a continuum by using a homogenization process to establish conservation equations for averaged quantities defined on a Representative Elementary Volume (REV). This model is applied to simulate cone calorimeter experiments of wood thermal decomposition in a nitrogen-rich environment, providing detailed insights into the complex interplay of chemical and physical processes during pyrolysis. The results highlight the model’s potential as a powerful tool to predict wood thermal decomposition in cases of thermally thick sample behavior, where secondary tars reactions play a key role in describing the entire dynamics of the pyrolysis process at high temperatures.
As a new type of energy that can meet the requirements of carbon neutrality, biomass has received wide a ention in recent years, and its rational and efficient thermal utilization can help reduce greenhouse gas emissions and establish an energy-saving, low-carbon energy system to promote sustainable development. In this paper, the current utilization and research status of plant-based biomass waste is comprehensively summarized from four aspects, namely component properties , industrial thermal utilization means, experiments and theoretical calculations. In addition, this paper summarizes the research progress in several aspects, such as microscopic experimental studies, macroscopic pyrolysis characterization, and multiscale theoretical model construction of biomass waste. However, due to the diversity and heterogeneity of biomass, there are still some challenges to extending the laboratory research results to large-scale industrial production, for which we also provide an outlook on future technological innovations and development directions in this research area.
The engineering of biochars with desired morphologies and pore structures is a far-reaching objective towards sustainable pore-dependent environmental technologies, such as water and soil remediation or catalysis. We hereby report a series of experiments that allow the direct following of the shape and porosity of single biochar particles during pyrolysis. Particles ~ 1–2 mm in diameter of unwashed and water-washed raw walnut shells were continuously 3D imaged during pyrolysis to 575 ℃ at a 10 K min ⁻¹ in Ar to obtain time- and temperature-resolved x-ray micro computed tomographies to a 0.82 μm resolution. Results showed visual evidence of a 30% and 70% v/v particle shrinkage for unwashed and washed samples, respectively. Particle swelling between 200 and 300 ℃ in the unwashed sample provided evidence of the softening of native biopolymers associated with lignin in untreated biomass. A purpose-defined parameter Λ shows the temperature-dependence of pore re-distribution towards the center of the particle to be linear for both samples. Λ was found to be 3.2 × 10 - 4 K - 1 in the washed sample, approximately 3.5 times faster than in the unwashed one. Such linear dependence is significantly slower than an exponential Arrhenius-like trend thereby providing a qualitative measure of the heat and mass transport phenomena limiting the chemical reactions in the porous medium. This evidence is key to resolving the pathways to the thermochemical decomposition of biomass leading to preparation of precision-engineered biochars.
Graphical Abstract
Bamboo and wood materials have the characteristics of low carbon and high strength, making them the besbuilding material for building green buildings. Compared to traditional building materials, the easy to burncharacteristic has become an obstacle to the promotion and widespread application of bamboo and wood materials, so it is urgent to study their combustion characteristics. "This article investigated the combustion characteristics of engineered bamboo at different heat fluxes, taking into account the smoldering and self-extinctioncharacteristics through cone calorimeter experiments. The combustion performance, mass loss rate, heat releaserate, etc, were studied, and the self-extinction phenomenon of the specimens was explored. The results indicatedthat the direction of heating had a certain impact on the combustion characteristics of glued laminated bamboo(LBL), and the fire resistance of parallel strand bamboo (PSB) was better than that of LBL. When the heat fluxexceeded 50 kW/m’, the color of the flame on the surface of the specimen would change from bright yellow tostrong orange, which is an important sign that the flame will self-extinguish. The self-extinction of flames atdifferent heat fluxes was caused by insufficient supply of combustible gas generated by bamboo pyrolysis, withslightly different specific reasons. The multi-layer structure of glued laminated bamboo also makes it moredifficult to self-extinguish than PSB, cross-laminated timber (CLT), and solid wood is the most prone to selfextinguish. The impact of adhesive layer delamination was not considered in this experiment, and furtherresearch is needed.
A 3 kg/h ablative pyrolysis reactor and a 1.5 kg/h fluid bed reactor were operated using pine wood as the feedstock over a temperature range of 450–600°C. Mass balances and product analyses were performed and product comparisons made. A similar gas/vapour product residence time of around 1 s was used to reduce differences. Product yields followed the same general trends with a maximum organics liquid yield around 500–515°C for both reactors (59.4 wt% organics at 515°C and 1.19 s residence time in the fluid bed reactor and 62.1 wt% organics at 502°C and 1.1 s residence time for the ablative reactor]. Char yields increased for the fluid bed reactor above 515°C, and also in the ablative pyrolysis reactor. The volatile content of the char products were higher for the ablative, compared to the results for the fluid bed chars which showed a continual rapid decrease. Water yields were similar in the range of 11–16 wt%. Gas yields were markedly lower in the ablative pyrolysis reactor suggesting a less severe environment for the vapour products. The gaseous product composition variation with temperature in the fluid bed suggests that secondary vapour cracking is more prevalent in the fluid bed than the ablative pyrolyser.
Many types of chemical pathways aimed at representing the primary process of biomass degradation have been published. These models include or ignore the possibility of the existence of an intermediate “Active” species or state. The purpose of this paper is to gather theoretical results and experimental observations intended to open the discussion on the possible existence and nature of such an intermediate.
The results of the modelling of the chemical and thermal behaviour of biomass undergoing a pyrolysis decomposition are first given. Simple experimental and visual observations associated with theoretical considerations based on heat transfer measurements lead then to the conclusion that the overall reaction is similar to a fusion with production of an intermediate liquid species. From kinetic rate constants derived from literature, it appears that it is not necessary to take into account such a liquid in thermogravimetric analysis (TGA) experiments, but that it cannot be ignored in high temperature ablative pyrolysis conditions.
At the end of the paper, a discussion is conducted on the possible chemical natures of these liquids, the evolved vapours and the condensed pyrolysis oils formed in a pyrolysis process. It is concluded that the primary liquids could be composed of dimers and higher oligomers derived from cellulose and lignin, while the vapours would be mainly monomers and monomer fragments from the cracking of oligomers in the liquid phase.
A co-current moving bed gasifier with internal recycle and separate combustion of pyrolysis gas has been developed with the aim of producing a design suitable for scaling-up downdraft gasifiers while maintaining a low tar content in the producer gas. Using wood chips with a moisture content of 7–9 wt% (db) as a fuel at a rate of 20 kg h−1, this system produced a gas with a heating value of 4500 kJ ms−3 and a very low tar content of < 0.1 gms−3.
A detailed mathematical model is presented for the temporal and spatial accurate modeling of solid-fluid reactions in porous particles for which volumetric reaction rate data is known a priori and both the porosity and the permeability of the particle are large enough to allow for continuous gas phase flow. The methodology is applied to the pyrolysis of spherically symmetric biomass particles by considering previously published kinetics schemes for both cellulose and wood. A parametric study is performed in order !o illustrate the effects of reactor temperature, heating rate, porosity, initial particle size and initial temperature on char yields and conversion times. It is observed that while high temperatures and fast heating rates minimize the production of char in both reactions, practical limits exist due to endothermic reactions, heat capacity and thermal diffusion. Three pyrolysis regimes are identified: 1) initial heating, 2) primary reaction at the effective pyrolysis temperature and 3) final heating. The relative durations of each regime are independent of the reactor temperature and are approximately 20%, 60% and 20% of the total conversion time, respectively. The results show that models which neglect the thermal and species boundary layers exterior to the particle will generally over predict both the pyrolysis rates and experimentally obtainable tar yields. An evaluation of the simulation results through comparisons with experimental data indicates that the wood pyrolysis kinetics is not accurate; particularly at high reactor temperatures.
The working hypothesis for the study was that the main part of the chlorine in biomass is in an inorganic form and therefore should not vaporize appreciably below the melting point of the corresponding salt (around 700 °C) because the vapor pressure over solid salt is negligible. In the study, biomass fuels (sugarcane trash, switch grass, lucerne, straw rape) were subjected to pyrolysis in a flow of nitrogen, and the weight of the residue and its chlorine content were measured and compared to the original fuel. Contrary to the hypothesis, the results showed that during pyrolysis of biomass 20−50% of the total chlorine evaporated already at 400 °C, although the majority of the chlorine was water soluble (in grass 93%) and therefore most probably ionic species. At 900 °C, 30−60% of the chlorine was still left in the char. At 200 °C less than 10% of chlorine had evaporated from the fuel, indicating that the chlorine is not associated with water. Another result was that there was no significant difference in the chlorine release between biomass and synthetic waste, i.e., a mixture of organic and inorganic chlorides. These results are contradictory with the starting hypothesis and can therefore have new implications for the use of these fuels in combustion and gasification processes.
Sugar cane bagasse, wheat straw, pine and cotton wood pyrolysis was studied by TGA in argon at heating rates of 5 and 20°C/min. The DTG (-dm/dt) peaks associated with the components of an untreated plant material are relatively wide and strongly overlap each other. A reduction in the amount of inorganic ions in the samples by simple water or dilute acid washing procedures resulted in sharper peaks with a better separation. The thermal decomposition of the major biomass components was described, more or less formally, by first order reactions and the DTG curves of the biomass samples were approximated by a linear combination of first order reactions. Good fits between the calculated and the experimental data and good reproducibility of the model parameters were achieved. The kinetic model applied here may serve as a starting point to build more complex models capable of describing the thermal behavior of plant materials during a thermal or thermochemical processing or burning. Theoretically, there is also a possibility to utilise this sort of calculation in the quantitative analysis of the cellulose and hemicellulose content of the lignocellulosic materials.
The pyrolysis of biomass is a thermal treatment which results in the production of char, liquid and gaseous products.
The aim of this paper is the study of the influence of kinetic and diffusion phenomena on the pyrolysis of biomass particles.
In our aboratory the pyrolysis process has been studied experimentally using thermogravimetric techniques and different scales of apparatus.
Experimental data suggest that the pyrolysis of fine particles can be controlled by kinetics. The rate of pyrolysis of biomass can be well represented by the sum of the corresponding rates for the main biomass components.
The effect of particle size has also been studied by measuring the weight-loss rate. For particles below 1 mm in diameter the process is controlled by kinetics, for larger particles the process is controlled by both heat transfer and primary and secondary pyrolysis reactions. As the temperature and the particle size increase the relative influence of transfer phenomena and secondary reactions increases.
The temperature profiles inside the particles during pyrolysis were also measured.
Upon heating, biomass materials undergo solid phase pyrolysis at relatively low temperatures (> 300 ºC), forming reactive volatile matter, a few permanent gas species and solid char. Unlike the various coals and peats, biomass materials typically lose 70% or more of their weight by the solid phase pyrolysis reactions. This transformation of the bulk of the biomass material from the solid to the vapor phase suggests the important role of vapor phase chemistry in the pyrolysis of biomass materials. Recognizing the highly reactive nature of the major constituents of the volatile matter, the significance of the vapor phase chemistry becomes even more apparent.
Recent studies and information on principal thermal reactions and products of cellulosic materials, and some of the proposed thermal conversion processes are reviewed to indicate the future possibilities and promises of this approach.
A transient, one-dimensional model which can simulate drying and pyrolysis of moist wood is presented. The porous wood is divided into four phases: solid, bound water, liquid water and gas phases. Conservation equations for energy and mass together with Darcy’s law for velocity and algebraic equations for the transport properties and physical properties are presented. The drying model is based on equilibrium between water vapor and bound or liquid water in the porous wood. For the thermal degradation process, two reaction schemes including a single one-step global and a multiple competitive reaction model which have been proposed in the literature, are included. A comparison between the two pyrolysis models has been made on dry wood and the results reveal that for the multiple reaction model, the heating rate and pyrolysis time have great influence on the ultimate char, tar and gas yields calculated. Simultaneously drying and pyrolysis of large wood particles are simulated. The effect of moisture content on the pyrolysis time is presented together with characteristic profiles for temperature, pressure and moisture distribution inside the particle. A temperature plateau can be observed at about 100°C where evaporation and condensation of liquid water takes place. The simulations show that the in-depth moisture content increases and exceeds the initial moisture content before evaporation. The reason for this increase is that when water evaporates in the front, some of it will be transported by convection and diffusion into the colder region and condensed.
A normative review of the literature describing the products, mechanisms, and rates of lignin and whole biomass pyrolysis is presented. The role of a complex sequence of competing solid- and vapor-phase pyrolysis pathways is elucidated.
The liquid products (tars or sirups) obtained from the fast pyrolysis of cellulosics show a wide variation in composition depending on the cellulosic feedstock used. Native cellulose in wood gives significant yields of hydroxyacetaldehyde and other low molecular weight oxygenated compounds but low yields of anhydrosugars, while highly altered micro-crystalline cellulose gives the reverse. Experimental results from fluidzed bed fast pyrolysis are given for poplar wood and for a number of types of cellulose produced by different processes. The effect on product nature and yields as a result of different pretreatments of the wood or cellulose before pyrolysis is also reported. From these observations, as well as from the variation of product yields with temperature for one cellulose product, possible mechanisms for the primary decomposition of cellulose are proposed. Two major parallel pathways appear to account for the yields of major products. The content and nature of inorganic salts and the degree of polymerization of the cellulose play an important role in determining the relative importance of these two decomposition pathways.
A pyrolysis kinetics model is presented which can be used for the prediction of pyrolysis oil yields for oak in an entrained-flow reactor. The parameters in the model were determined by a nonlinear least-squares computer code and experimental results. An interpretation of the model predictions is included. The maximum oil yield obtained experimentally was 51%. The model predicts that a maximum oil yield of 63% is possible at a temperature of 550 degree C (the highest temperature run to date) at a much higher inlet gas rate than has been used.
When wood is heated at elevated temperatures, it will show a permanent loss of strength resulting from chemical changes in its components. The thermal decomposition can start at temperatures below 100°C if wood is heated for an extended period of time. Figure 1 shows that wood heated at 120° loses 10% of its strength in about one month, but i t takes only one week to obtain the same loss of strength if it is heated at 140° (1). Heating at higher temperatures gives volatile decomposition products and a charred residue. The pyrolytic reactions and products control the combustion process and relate to the problems of cellulosic fires, chemical conversion of cellulosic wastes and utilization of wood residues as an alternative energy source. In our laboratory, the pyrolytic reactions of wood and its major components have been investigated by a variety of analytical methods. Thermal analysis of cottonwood and its
A heat radiation reactor was used to study the mechanism of cellulose rapid pyrolysis in the present paper. Combined with gas chromatography-mass spectrometry analysis on bio-oil, experimental results showed that the production rate of hydroxyacetaldehyde and 1-hydroxy-2-propanone, as well as their proportions in bio-oil, increased with the reaction temperature in the case of short gas residence time. The formation of the above two products was shown to be competitive with levoglucosan formation from active cellulose. In addition, a modified cellulose pyrolysis model based on the Brodio-Shafizadeh model was proposed to describe this competitive phenomenon. Major products' formation was simulated with this modified model, which was in good agreement with the experimental results.
The influence from structural changes, heat transfer properties of dry wood and pyrolysis mechanism on the pyrolysis of large wood particles were studied. Measurements of temperature distribution and mass loss were performed on cylindrical samples of dry birch wood during pyrolysis in an inert atmosphere at 700°C. A model of wood pyrolysis was modified to include structural changes. Comparisons of measurements and model simulations show that the inclusion of a shrinking model reduces the time of pyrolysis substantially. The varying interior heating rate was found to influence the choice of pyrolysis mechanism. Of four pyrolysis mechanisms found in literature, only one was found to be in agreement with the measurements.
This paper examines the effects of intraparticle heat and mass transfer on the devolatilization of millimeter-sized biomass particles under conditions similar to those found in commercial coal-fired boilers. A computational model is presented that accounts for intraparticle heat and mass transfer by diffusion and advection during particle heating, drying, and devolatilization. To evaluate the model, devolatilization experiments under high-temperature and high-heating rate conditions were conducted using the Multifuel Combustor at Sandia National Laboratories. Measurements of mass-loss and changes in particle size for millimeter-sized alfalfa and wood particles are presented as a function of reactor residence time. For millimeter-sized particles, both fuels completely devolatilized in approximately 1 s with rapid initial mass loss. The total volatile yield of the wood was 92% on a dry, ash-free basis, significantly higher than that reported by a standard ASTM test, indicating dependence of the ultimate yield on local conditions. Particles for both fuels shrink significantly and become less dense during devolatilization. The comprehensive model accurately predicts the devolatilization behavior of millimeter-sized biomass particles; these measurements could not be reproduced with a simple lumped model that ignores intraparticle transport effects. The comprehensive model is used to examine the effects of particle size and moisture content on devolatilization under conditions representative of those found in coal boilers. Biomass particles of radii up to 2 mm and moisture content up to 50% are considered. As expected, intraparticle heat and mass effects are more significant for larger particles. These effects can significantly delay particle heating and devolatilization; for example, intraparticle effects delay the heating and devolatilization of millimeter-size particles by as much as several seconds for a particle with a 1.5-mm radius compared to predictions of a lumped model. This delay is significant considering the short residence times of commercial boilers and should be accounted for in computational models used to evaluate the effects of biomass-coal cofiring on boiler performance.
We present here a decoupling technique to tackle the entanglement of the nonlinear boundary condition and the movement of the char/virgin front for a thermal pyrolysis model for charring materials. Standard numerical techniques to solve moving front problems — often referred to as Stefan problems — encounter difficulties when dealing with nonlinear boundaries. While special integral methods have been developed to solve this problem, they suffer from several limitations which the technique described here overcomes. The newly developed technique is compared with the exact analytical solutions for some simple ideal situations which demonstrate that the numerical method is capable of producing accurate numerical solutions. The pyrolysis model is also used to simulate the mass loss process from a white pine sample exposed to a constant radiative flux in a nitrogen atmosphere. Comparison with experimental results demonstrates that the predictions of mass loss rates and temperature profile within the solid material are in good agreement with the experiment. Copyright © 1999 John Wiley & Sons, Ltd.
Biomass pyrolysis studies were conducted using both a thermogravimetric analyser and a packed-bed pyrolyser. Each kind of biomass has a characteristic pyrolysis behaviour which is explained based on its individual component characteristics. Studies on isolated biomass components as well as synthetic biomass show that the interactions among the components are not of as much significance as the composition of the biomass. Direct summative correlations based on biomass component pyrolysis adequately explain both the pyrolysis characteristics and product distribution of biomass. It is inferred that there is no detectable interaction among the components during pyrolysis in either the thermogravimetric analyser or the packed-bed pyrolyser. However, ash present in biomass seems to have a strong influence on both the pyrolysis characteristics and the product distribution.
The effects of cations on the yields of char, tar, light oils, and total gases from rapid pyrolysis of beech wood were studied. Raw wood, acid washed wood, and wood impregnated with potassium, sodium, and calcium cations were pyrolyzed in 1 atm pressure of helium at 1000°C s−1 heating rate to a peak temperature of ≈ 1000°C. Experiments were carried out in an electrical screen heater reactor, and the yields of products were determined as a function of pyrolysis peak temperature. Acid washed wood samples gave the highest tar yield (about 61% by weight of the original wood), whereas wood samples impregnated with potassium or sodium cations gave the lowest yield of tar (32 wt%). The char yield from acid washed wood samples was lower (about 6 wt%), and it was higher for raw wood and for wood samples impregnated with different cations (10–15%). The maximum gas yield was lower at ≈ 34 wt% for acid washed wood and much higher (≈ 58 wt%) for the wood samples impregnated with potassium and sodium cations. These results, as expected, confirm the marked catalytic effects of cations on the post-pyrolysis cracking reactions of tar (the major product of wood pyrolysis) and the formation of char and gaseous products via cracking reactions of tar. In all these cases, sodium and potassium cations showed a stronger effect than calcium cations. The tar molecular weight was measured for wood samples impregnated with different cations. Tar molecular weight decreased with addition of cations to the wood particles, whereas it remained relatively constant with pyrolysis temperature. The tar molecular weight dropped from about Mw = 300 amu and Mn = 155 amu for raw and acid washed woods to about Mw = 190 amu and Mn = 100 amu for woods impregnated with potassium or sodium cations.
A Setaram DSC in conjunction with stainless steel pressure vessels was used to investigate the effects of pressure and purge gas flow rate (gas phase residence time) on the heat demands of cellulose pyrolysis. High pressure and low flow rate reduce the heat of pyrolysis and increase char formation. Experiments were conducted to investigate the pyrolysis reactions of anhydrocellulose and levoglucosan, the two major intermediate products in cellulose pyrolysis. Separate models for the degradation of each intermediate were postulated and combined to form a detailed mechanistic model for cellulose pyrolysis. The model explains all the observed effects of pressure and flow rate.
Rice hulls were pyrolyzed in a thermogravimetric analyzer in a helium atmosphere to determine the kinetic parameters of devolatilization reactions. The pyrolysis experiments were conducted by heating rice hulls from room temperature to 1173 K at constant heating rates of 3, 10, 30, 60, and 100 K/min. The global mass loss during rice hull pyrolysis was successfully simulated by a combination of four independent parallel reactions, the decompositions of four major components in rice hulls: moisture, hemicellulose, cellulose, and lignin. The activation energy for the decomposition of the nonmoisture components was in the order cellulose > hemicellulose > lignin. It was also found in the present study that the pyrolytic behaviors were significantly influenced by water wash prior to pyrolysis. The water wash elevates the peak temperature and the activation energy for the decomposition of each component of rice hulls. The volatile yields resulting from cellulose and hemicellulose decompositions during rice hull pyrolysis increase due to the water treatment, whereas those from lignin decomposition and the char yield decrease.
The homogeneous vapor phase cracking of newly formed wood pyrolysis tar was studied at low molar concentrations as a function of temperature (773 - 1.073 K), at residence times of 0.9 - 2.2 s. Tar conversions ranged from about 5 to 88%. The tars were generated by low heating rate (0.2 K/s) pyrolysis of --2 cm deep beds of sweet gum hardwood, and then rapidly conveyed to an adjacent reactor for controlled thermal treatment. Quantitative yields and kinetics were obtained for tar cracking and resulting product formation. The major tar conversion product was carbon monoxide, which accounted for over two-thirds of the tar lost at high severities. Corresponding ethylene and methane yields were each about 10% of the converted tar. Coke formation was negligible and weight-average tar molecular weight declined with increasing tar conversion.
Improved experimental techniques are described, using a wire mesh reactor; for determining the pyrolysis yields of lignocellulosic materials. In this apparatus pyrolysis tars are rapidly swept from the hot zone of the reactor and quenched, secondary reactions are thereby greatly diminished. Particular emphasis is placed upon the measurement of the pyrolysis yields for sugar cane bagasse, an abundant agricultural waste product. The role of the important pyrolysis parameters, peak temperature and heating rate, in defining the ultimate tar yield is investigated, with the value for bagasse being 54.6% at 500 C and 1,000 C/s. The pyrolysis yields, under similar conditions, of another biomass material, silver birch, are also reported and compared to those of bagasse.
In recent years there has been a growing interest in using wood, bark and foliage for chemical biomass conversion studies.1 The reasons are understandable since forests represent one of the largest sources of renewable biomass still available to mankind. Also, the Forest Product Industries provide a constant, collected source of potential thermochemical conversion material such as tops, limbs, bark and foliage not required for lumber or pulp. This potential will increase dramatically if plans to introduce whole tree logging materialize. Unfortunately, many scientists have been attracted to this potential biomass who are unfamiliar with the wide variation among and between tree species. To many wood is wood and they make little attempt to define the sample on which valuable scientific research is done. Borrowing a sentence from the Basic Coal Sciences Project Advisory Report2 and substituting wood for coal, the following statement emerges and describes the current situation concisely: ‘Considerable basic research has been done on a wide range of wood samples for various purposes, yet much of this previous research cannot be correlated since little, if any comparisons can be drawn from the samples used’. The Estes Park conference unanimously endorsed the need for reviewers and authors to be aware of tree variability and to define all research samples in such a way that other scientists may be able to calibrate and correlate their own research results.
Seeking to systemalically identify and organize the physical and chemical properties of biomass particles for combustion in furnaces, an attempt is made here to theoretically describe the temporal change in mass of a burning particle of an organic solid. The development involves a series of simple models to highlight the mechanisms involved, the physical and chemical properties of concern and the expected results. Although many simplifying assumptions are made, the properties identified, the parameters which evolved and the final functional form of the results are expected to becorrect.
A mathematical model based on unreacted-core shrinking model is developed to describe the pyrolysis phenomena of the cellulosic materials in the temperature range of 700–1470 K. The relative importance of each model parameter is studied by applying the sensitivity analysis. The heat transfer control region and kinetic reaction control region are obtained from the developed model. The shift of controlling mechanism is dependent on the particle size and the wall temperature. The effect of heat of reaction on the temperature of the particle is also discussed.
Single, thermally thick particles of lodgepole pinewood were pyrolyzed under well-defined conditions of industrial importance. Particle thickness, heating level, moisture content, density, and grain axis relative to one-dimensional heating were varied using a Box-Behnken experimental design. Gross product fractions, as well as components therein, were measured and the batch yields were correlated with second-order polynominals. The empirical equations correlating the batch yields, together with their prediction uncertainties, are presented and are suitable for use in simulations of wood combustion and thermal conversion. Comparison of large particle pyrolysis product distributions to other studies of small-particle pyrolysis yields shows the trends with particle size to be consistent. Tar yield minima depend on both particle size and heating rate. Gas yield is dependent on both particle size and heating intensity. Because some process controllables were found to alter product yields from large particles in a multiplicative way, rather than an additive way, suggestions for future experiments are made.
Thermogravimetric data on the devolatilization rate of beech wood are re-examined with the aim of incorporating the effects of high heating rates (up to 108Kmin−1) in the global kinetics. The mechanism consisting of three independent parallel reactions, first-order in the amount of volatiles released from pseudo-components with chief contributions from hemicellulose, cellulose and lignin, is considered first. It is found that the set of activation energies estimated by Gronli et al. [M.G. Gronli, G. Varhegyi, C. Di Blasi, Ind. Eng. Chem. Res. 41 (2002) 4201–4208] (100, 236 and 46kJmol−1, respectively) for one slow heating rate results in very high deviations between predicted and measured rate curves. The agreement is significantly improved by a new set of data consisting of activation energies of 147, 193 and 181kJmol−1, respectively. In this case, the overlap is reduced between the reaction rates of the three pseudo-components whose chemical composition is also modified. In particular, instead of a slow decomposition rate over a broad range of temperatures, the activity of the third reaction is mainly explicated along the high-temperature (tail) region of the weight loss curves. The performances of more simplified mechanisms are also evaluated. One-step mechanisms, using literature values for the kinetic constants, produce large errors on either the conversion time (activation energy of 103kJmol−1) or the maximum devolatilization rate (activation energy of 149kJmol−1). On the other hand, these parameters are well predicted by two parallel reactions, with activation energies of 147 and 149kJmol−1.
A comparison between the thermal decomposition of almond shells and their components (holocellulose and lignin) was carried out, considering the yields of the most important products, under flash conditions, and the decomposition kinetics.The yields of the main gaseous products obtained in the fast pyrolysis of almond shells can be reproduced from the yields obtained with holocellulose and lignin. The best results were obtained with CO, water and CO2. The differences were greater with the minor hydrocarbons, CH4, C2H6, C2H4, etc.The kinetics of the slow thermal decomposition (TG-DTG) of almond shells cannot be reproduced by the sum of lignin and holocellulose. The cellulose from almond shells decomposes at lower temperatures than almond shells, and the behavior of isolated lignin is very different from that found when it forms part of the raw material, proving the importance of the interactions between its components.
Drying and devolatilization are studied at combustion temperatures. The surface temperature of particles at the end of drying can significantly exceed the temperature when devolatilization starts, implying that drying and pyrolysis may partly overlap. Devolatilization is controlled by heat transfer, when the particle size is large. The critical particle size at which heat transfer dominates chemical kinetics is discussed. A model for calculating the intrinsic rate of generation of volatiles in the regime of heat transfer control is presented. A novel isotherm migration method is used for the computation of simultaneous drying and pyrolysis inside a fuel particle. It applies to the study of heat transfer in a one-dimensional geometry with moving phase-change boundaries, internal fluid flow and mass generation, including steep temperature and density profiles, as frequently encountered in combustion.
In this paper, the weight loss of four different woods during vacuum pyrolysis at constant temperature and at constant heating rate are reported. Based on these results, an empirical model of the weight loss rate as a function of temperature has been developed. The model assumes that wood is composed of three major components: cellulose, lignin, and a mixture of hemicellulose and volatiles. Under vacuum conditions, it is also assumed that the pyrolysis of these components proceeds independently of the others. The resulting kinetic parameters can be used to predict volatilization rates of wood as a function of temperature in a vacuum. The model may also be used to estimate the quantities of each of the main components initially present in an unknown wood sample.
A lumped-parameter kinetic model is applied to simulate the pyrolysis of lignocellulosic particles, exposed to a high temperature environment. Physical processes account for radiative, conductive and convective heat transport, diffusion and convection of volatile species and pressure and velocity variations across a two-dimensional (2-D) , anisotropic, variable property medium. The dynamics of particle degradation are found to be strongly affected by the grain structure of the solid. A comparison is made between the total heat transferred to the virgin solid (conduction minus convection) along and across the grain. Notwithstanding the lower thermal conductivities, because of the concomitant slower convective transport (lower gas permeabilities) , the largest contribution is that across the solid grain. The role played by convective heat transport is successively less important as the particle size is increased. Finally, the 2-D and the widely applied one-dimensional (1-D) predictions are compared.
Pyrolysis experiments in a thermogravimetric analyser and in a muffle furnace were carried out with spruce and beech wood. The particle size of the samples of spruce wood was varied in the range 0.5–20 mm and the heating rate was varied in the range 5–60 K/min. Additionally, drop-in experiments in the muffle furnace were carried out with both spruce and beech wood. These experimental data were compared with the results from calculation of pyrolysis of ‘large’ particles with the simulation program parsim. Agreement could only be obtained when the tar decomposition outside of the particle was taken into account. The pre-exponential factor and the ultimate yield for cracking of tar from beech wood are given.
This work deals with the kinetic analysis of data obtained in thermobalance. It consists of a review of kinetic models used for material decomposition, and also of the methods used for the analysis. The topics presented comprise numerical problems related with kinetic analysis, best conditions for a kinetic run, discussion about correlation vs. actual models, nth order models, more complex models (models using a great number of reactions, models using various fractions), calibration of the temperature, position of the thermocouple, sample mass and particle size. Other topics treated are the validation of kinetic models using MS data and the different models available for kinetic studies in thermobalance.
Release of volatiles of non-spherical pine wood particles was analysed by means of continuous measurements of the CO2 and O2 concentrations obtained after the complete combustion of the volatiles and from flame extinction times. The effect of the atmosphere used for devolatilisation was tested. The volatiles' evolution was nearly identical using air or N2 as fluidising gas. The devolatilisation times increased with increasing the equivalent particle diameter, but there was an important scattering in the results. The data dispersion greatly decreased when the shape factor of the wood particles was considered. The devolatilisation times were fitted to a power-law relation replacing the particle diameter by the equivalent particle diameter multiplied by the shape factor. The effect of the moisture content was studied by analysis of the devolatilisation process of pine wood particles of the same size and different moisture contents (0–50%). As the moisture content of the wood particles increased the devolatilisation rate of combustible volatiles decreased and was more uniform along the devolatilisation time.
The catalytic effect of pH-neutral inorganic salts on the pyrolysis temperature and on the product distribution was studied by fractionated pyrolysis followed by GC/MS and GC/FID and by thermogravimetric analysis (TGA) of cold-water-washed hornbeam wood. Sodium and potassium chloride have a remarkable effect on the pyrolysis temperature and on the product distribution, whereas calcium chloride only changes the low temperature degradation of hornbeam wood and the product distribution is nearly unchanged compared with water-washed hornbeam wood. All studied potassium salts (KCl, KHCO3, and K2SO4) decrease the amount of levoglucosan the order of magnitude being dependent on the anion: chloride has a more pronounced effect than sulphate, and sulphate a more pronounced effect than bicarbonate. The thermal degradation of three different wood species (hornbeam, walnut and scots pine) was investigated by analysis of thermogravimetric/mass spectrometric pyrolysis. Commonly used model substances for the main components of wood, like xylan, pure cellulose or filter pulp, were found to be unreliable for the evaluation of formal kinetic parameters that are able to describe the pyrolysis of wood. A method for the individual evaluation of formal kinetic parameters for the main components of wood was used, that uses specific ion fragments from lignin degradation products to study the lignin degradation. Coniferous lignin is thermally more stable than deciduous lignin, and the latter produces smaller char yields. The differences in wood species mainly result in different degradation rates for the lignin and for the early stages of the hemicellulose degradation.
A kinetic study of the pyrolysis of municipal solid waste (MSW) in a fluidized bed reactor was carried out. The MSW pellets are discharged onto the fluidized sand bed; in the upper part of the reactor the volatiles evolved from primary reactions underwent secondary cracking reactions. A correlation model was applied to simulate the primary and secondary reactions as well as the heat transfer process. The experimental yields of the total gases obtained in 49 runs performed at 700, 750, 800 and 850 °C fitted satisfactorily using a flexible simplex method. The values of the kinetic parameters of secondary reaction, the heat transfer coefficient from the bed to the sample and the ratio “secondary gas yield/primary tars yield” were optimised. The values of the secondary kinetic parameters, which showed a great inter-relation with those of the primary reactions, were within the range of the values proposed in literature for other biomass tar cracking.
A kinetically based prediction model for the production of organic liquids from the flash pyrolysis of biomass is proposed. Wood or other biomass is assumed to be decomposed according to two parallel reactions yielding liquid tar and ( gas + char) The tar is then assumed to further react by secondary homogeneous reactions to form mainly gas as a productThe model provides a very good agreement with the experimental results obtained using a pilot plant fluidized bed pyrolysis reactorThe proposed model is shown to be able to predict the organic liquid yield as a function of the operating parameters of the process, within the optimal conditions for maximizing the tar yields, and the reaction rate constants compare reasonably well with those reported in the literature
A novel moving and stirred bed reactor with a high heat transfer capacity has been operated to achieve the thermal decomposition of used tyre particles under vacuum. The overall heat transfer coefficient determined in this reactor reaches 200–250 W m−2K−1, a value exceeding the levels obtained in conventional rotary kilns and multiple hearth furnaces. In order to design large scale stirred bed vacuum pyrolysis reactors, both experimental and theoretical studies were carried out to understand the heat transfer mechanism and to determine the heat transfer coefficient in the reactor as a function of the operating conditions. In this work, the heat transfer coefficients under different agitation speeds up to 22.5 rpm were measured. The heat transfer coefficient was found to increase with the agitation speed, proportionally to (1/tmix)1/2. A Schliinder's modified model was used to describe the correlation between the heat transfer coefficient and the operating conditions. Calculation of the partial heat transfer coefficients during the three pyrolysis evolution periods revealed the influence of the chemical reactions, the phase change and the feedstock thermal property variation on the overall heat transfer coefficient during the vacuum pyrolysis of tyre particles.
Flash pyrolysis of wood in a circulating fluidized bed is studied. The results of a comprehensive gas-solid reaction model are used successfully in analysing the system. The changes in the structure, the transient nature of heat and mass transfer and the reaction scheme are accounted for. All the structural parameters and thermophysical properties are used as continuously changing variables.
The modelling of the spread of fire and its extinguishment still represents a significant challenge. As part of a combined experimental and computational study of fires we have developed a general Computational Fluid Dynamics (CFD) model of fire spread and extinguishment. The primary objective was to produce a flexible computational tool which can be used by engineers and scientists for design or research purposes. The present paper deals with the description and validation of a solid pyrolysis model which has been applied, as a sub-model, in this general computer fire code. The pyrolysis model has been formulated using the heat-balance integral method. The model can be applied to slabs of char forming solids, such as wood, as well as non-charring thermoplastic materials, such as PMMA. Results are compared with analytical solutions, numerical simulations and experimental data. In all cases the integral model performs well. © 1997 by John Wiley & Sons, Ltd.
A comprehensive mathematical model of wood pyrolysis, based on the unreacted-core-shrinking approximation, is used to assess the role played by the description of the kinetics for a one-step global reaction. The more accurate model, which was previously subjected to experimental validation, includes a first-order Arrhenius rate, whereas the simplified one uses the assumption of constant (assigned) temperature, T-p, at the pyrolysis front. Both models predict qualitatively similar particle dynamics. Extensive simulations, carried out by varying the parameters of the kinetic models, the external heating conditions, and the particle size, indicate that the unknown parameter T-p, though comprised in the range of experimental values, should not be chosen coincident with the pyrolysis temperatures predicted by the finite-rate model. However, a range of T-p values can be determined that produces chief process characteristics, such as maximum devolatilization rate and conversion time, very close to those of the finite-rate model. In this way, acceptable agreement is also obtained between predicted and measured integral and differential mass loss curves of thick wood exposed to radiative heating.
A new integral thermal pyrolysis model for the transient pyrolysis of charring and on-charring materials has been developed and evaluated by comparison of the results with exact solutions. The purpose for the development of this simple model has been the desire for predicting pyrolysis histories of materials exposed to pre heat fluxes by using “equivalent” properties tailored to the present model and common flammability test measurements. The pyrolyzing material is divided into a char layer and a unpyrolyzed (virgin) layer where the material has not yet pyrolyzed. These two layers are separated by an isothermal interface which is at a pyrolysis temperature (characteristic of the material). At this interface, heat is transferred to the virgin layer, causing further pyrolysis of the material (namely a thermal pyrolysis model is used). A one-dimensional transient heat conduction model is used to predict the heat transfer within the material. Exponential temperature profiles were assumed for the heat conduction model. Using a rwo-equation 9-moment method, the original partial differential equations were transformed into a set of two ordinary differential equations for each layer. These equations were numerically salved to I) determine the pyrolysis rate. regression depth and surface temperature, and 2) establish a dimensional and sensitivity analysis. The model has been shown to be very accurate (errors ~ 2%) from comparisons between numerical results and exact solutions. Despite the neglect of derailed chemical kinetic (Arrhenius) pyrolysis expressions, the accuracy of the integral model together with its simplicity has allowed the deduction of pyrolysis properties of materials by using common flammability test data as it ';ill be proved in a subsequent paper.
Fluoroptic temperature measurement has been applied to determine the external heat transfer coefficient of particles flowing along the surface of a rotating cone reactor, specified by a half cone top angle of 45° and a maximum diameter of 68 cm, which has been designed for flash pyrolysis of biomass. Two different hydrodynamic regimes have been considered. Both, the cooling of a very dilute stream of hot particles, flowing freely along the cold cone wall and the cooling of hot particles in a very dense cold sand flow (moving bed regime) were studied. In the very dilute regime (without sand supply), the derived heat transfer coefficients are in the range of 500–1000 W m−2 K−1 and display a minimum as a function of the cone rotation frequency. Experiments at cone rotation frequencies of 3.77–5.28 Hz show that heat transfer coefficients for small particles (average particle diameters of 159 and 284 μm) are reasonably well predicted by the correlation of Ranz and Marshall [W.E. Ranz, W.R. Marshall, Evaporation from drops: Part 2, Chem. Eng. Pr. 48 (1952) 173] for heat transfer by gas phase convection to a non-spinning sphere in free flight. Contrary, larger particles with an average diameter of 428 μm show significantly higher heat transfer coefficients than expected on basis of the Ranz and Marshall equation. This is explained by a changing flow pattern of the particles over the conical surface and the consequences for the slip velocity between gas phase and particles. Large deviations from the Ranz–Marshall equation at a cone rotation frequency of 3.01 Hz are explained in terms of an increased contact with the wall resulting in a higher contribution of conduction to the total heat transport. For sample particles in a flow of sand with an average diameter of 350 μm, the determined heat transfer coefficient gradually decreases as a function of the cone rotation frequency; it remains constant however for coarse sand (750 μm). These phenomena have been explained in terms of variation in density of the gas/solids emulsion.
In order to investigate vapour phase cracking of tar from pyrolysis of spruce wood, experiments with small particles of spruce wood (0.5–1.0mm) were carried out both in a thermogravimetric analyser (TGA) and in a coupling of the TGA with a consecutive tubular reactor. In all experiments, the TGA was heated from 105 to 1050°C at a heating rate of 5Kmin−1. The tubular reactor was operated at temperatures of 600, 700 and 800°C at different residence times, these being achieved by providing the reactor with three independent heating zones. For the tubular reactor, a one-dimensional flow model was employed which took axial dispersion and the non-isothermal state into consideration. It was found that different types of tar are produced from pyrolysis of spruce wood. One of these types does not crack, for the other types, kinetic parameters for tar cracking and distribution coefficients for the formation of product gases were determined.
Pyrolysis of maize is experimentally investigated in a bench-scale rotary kiln in semi-continuous operation. The operational parameters varied are the temperature (450–800°C), the solids residence time (7–20min) and the solids space time (117–417min). Mathematical modeling includes (a) the determination of suitable functions describing the material properties, (b) the selection of a reaction scheme and a formal kinetics approach in order to calculate the source terms of the balance equations, and (c) the solution of the so defined system of differential equations. Stoichiometric coefficients and formal kinetic parameters are estimated from thermoanalytic and rotary kiln experiments by regression. The results show the expected strong influence of pyrolysis temperature and a noticeable influence of space velocity. The solids residence time shows no significant influence on product yields. The model results describe well the experimental data; however, the influence of space velocity is slightly overpredicted.